Step 2: Gear Train

The Lego motor spins at roughly 360 rpm which is quite slow so in order to speed this up we utilize a gear train. Below is a picture of the assembly. The end of the gear train is on the upper left and it will be the part that is attached to the spinning magnet bar.

Step 3: Build a frame

You want to build a frame to support a cup so in this design I built it using Lego pieces. What is important though is that your frame is sturdy enough to hold a cup with liquid and has some clearance for the spinning magnet mechanism. I used a Lego connector that looks like a T shape to attach the magnet onto the gear train. I also used some tape to secure it. When the setup is complete you should be able to place the bar magnet on top and it will lock into place. I chose neodymium magnets because they were strong.

ok. so as someone who owns a real hotplate / stirrer, i have one little detail everyone seems to be missing. that bottom magnet that is attached to the motor? Its not a bar magnet. Its a ring magnet. you want a ring that is about 3 inches outside diameter. epoxy it to a metal circle which you attach to a suitable motor. make sure it is centered or bad things will happen.

I made this a day or two ago, great instructable! I didn't use exactly called for, but it worked. Problem is with making one of these it that you HAVE TO HAVE the perfect magnets. Most magnets I had were too weak or too bulky. Anther problem with making one is that the legos are hard to balance on a rod, even with adding a T-bar. and conmorse is right. Unless you get a magnet meant for this, magnet particles and possibly paint could get in it. Fun, but impractical.

I actually prefer the ovoid (egg) shaped ones, as the bottom of my some of my mugs are not flat in the middle and the other stir bars don't spin as fast. Plus, they are small enough that they work in all sizes of cups.

Teflon is non-reactive (for high acidity drinks like orange juice) as well as highly resistant to heat (coffee) although the magnet doesn't like the hot temperatures... But they are cheap enough and even with abuse they last for years and years.

I have a T shaped Lego piece attached to the motor shaft. I taped a strong bar magnet to that piece. Its shown in the second and third picture of step 3. Then the red plate is placed over and a freely moving magnet is placed on top. The magnetic attraction of the bottom magnet causes the top one to spin.

I've been thinking about building my own magnetic stirring device for a while now, but I must admit using legos never occurred to me...thanks for the time saving idea! Oh, and good choice on the music, Paul Van Dyk is simply mesmerizing.

To prevent someone from swallowing the stir rod take a disc shaped magnet and hold it to the bottom of the cup. The indentation that is likely in the cup will hide the magnet, and both magnets should stick in place. If the stir rod isn't a strong enough magnet to hold the second magnet to the bottom of the cup, then use the second magnet to drag the stir rod out of the cup before drinking.

erm a MUCH easier and better one to do would be simply have an inversed "T" where the "-" part is the magnet and the "|" part is a large piece of metal/plastic, if the magnet is plastic coated so it is non-toxic and the attachment doesnt use toxic chemicals then it should still be drinkable, as the handle is vertically attached (perpendicular) it will be in the centre of the vortex created by the magnet and so will not creating any detrimental effect to its speed and being easy to remove. This also leads to a possibility of making it with larger bottles as you could add fins to the handle to create flow.

Umm... read my post again, I'm not talking about anythnig that goes in the cup, or gets attached to the bottom. Just something that you can sit there as a quick fix for a mentioned problem in the instructable. I'm talking about after, so your guest doesn't accidentally swallow the rod. Also, it's not my instructable, and I didn't mention the stirring portions of the instructable at all. Also also, adding fins will not help in the slightest. The high rpm is what creates the vortex, add fins and you'll add too much resistance. You'll encounter something known as "spin out" which is when the magnetic coupling is not as strong as the hydraulic resistance, meaning your finned T thing will lethargically lurch around in the cup. Stick with the sciences and you'll encounter actual high speed electronic stirrers, you'll see a total lack of fins on them.

I hate to take sides, but negafen is right about spin out. I maxed out my device at around 3000 rpm. The vortex is amazing, it reaches the bottom completely as you could see in the video. It mixed 3 tablespoons of ice tea mix in a few seconds (not that I'm going to drink it). I gave the inversed T idea a shot and the bar is very unstable, sorry thinker :-(. The fins approach I'm not even going to try because at 3000 rpm I know I would lose coupling.

ahh reet no problemo, when i posted that i wasnt sure whether it would create drag on it or not but now i think about it it does make sense >_< and yeah, i get what you mean about the bar being unstable after i tried my own idea. thanks for readin it tho,